In addition to cable television (CATV), many cable system operators provide high speed internet access, video on demand (VOD), Voice over IP (VoIP) telephone and numerous other services to subscribers. To provide such services, cable system operators must manage and maintain increasingly complex networks. FIG. 1 is a block diagram showing an example of such a network. A national head end may include elements such as VOD servers, servers for receiving and encapsulating programming content, management servers, etc. The national head end communicates with multiple regional head ends over a national backbone network, with the regional head ends also including facilities for VOD and programming reception/encapsulation. Each regional head end communicates over a regional access network with multiple hubs. Each hub includes a cable modem termination system (CMTS), devices for quadrature amplitude modulation/demodulation (QAM), and other elements.
From the hubs, individual homes or other subscriber locations are reached via a hybrid fiber coax (HFC) access network. The fiber optic portion of the HFC access network includes multiple nodes on a fiber optic ring. The coaxial portion of the HFC access network includes coaxial feeder lines extending from those nodes. Drop coaxial cables extend from taps in the feeder cables and connect to the subscriber premises. Amplifiers are distributed along the coaxial feeder cables. Alternating current (AC) power may also be input into the feeder cables so as to provide a power source for the amplifiers. For simplicity, FIG. 1 only shows a very small part of the coaxial portion of an HFC network associated with a single hub. In actuality, the coaxial cable plants associated with hubs may be the largest part of the system, and there may be many subscribers receiving service through a particular hub.
Communication through a coaxial cable can be affected in many ways. As but one example, temperature changes can affect signal quality in coaxial cables. To detect, prevent and correct communication problems, signal quality measurements from the coaxial part of an HFC network can be very useful. Unfortunately, obtaining such measurements for a large portion of a coaxial cable network over a prolonged period has not been practical. Existing test equipment is relatively expensive, and in many cases a field service technician must be dispatched to take measurements. Some set top boxes and cable modems can measure certain signal parameters, but only over a few channels at a time and at relatively infrequent intervals. Moreover, signal measurements from inside a subscriber premises may not be indicative of a network problem. For example, signal degradation within a subscriber location could be affected by a splitter or other subscriber-installed component and not by a systemic network condition.